The invention relates to a closure with pressure-compensating valve for the filling hole of a liquid container, with a bung-type socket of soft elastic material which fits into the round hole and has a flange-like outer bearing portion, a circumferential sealing portion sealingly receiving the rim of the hole, a circumferential snap-action portion engaging the inside of the rim of the hole from behind, and a central orifice, and with a valve element which can be manually moved into position and. which occupies in the central orifice a sealing closed position and a pressure-compensating position, in which the interior of the container is in communication with the atmosphere.
Such a closure is known from German Patent DE 4219571 C2. It can be used for containers in the form of kegs, mini-kegs (party kegs) or cans, from which liquids, especially beverages, are drawn without pressure or under pressure. It is usable in particular for party kegs for beer.
As set forth in the introduction of German Patent DE 3345619 C2, the snap-action and sealing properties of the bung-type socket of the closure are subject to considerable and in some cases conflicting requirements. To meet these, DE 3345619 C2 proposes making the bung-type socket of a soft part and a hard part, which encloses the soft part in the manner of a cage and through which the soft part penetrates at the apertures between the bars of the cage. The flange-like outside bearing portion of the soft part is stiffened with a flange on the hard part, and outwardly protruding snap catches are provided on the hard part.
A disadvantage of this bung-type socket is its complex structure, which necessitates injection molding of the hard part in a first step, after which the soft part is injection-molded thereonto in a second step. Because of the fact that hard and soft portions alternate over the circumference of the bung-type socket, a leaktightness problem can occur at the edges therebetween. In addition, deposits can accumulate here, with the potential for undesired bacterial growth.